Cryptophycins are novel macrolides first isolated from blue-green algae (Nostoc sp. GSV22 and Nostoc sp. ATCC 53789) and are potent tumor selective cytotoxins in vivo. Many syntheses of the major natural products, cryptophycins 1–4, and a wide range of analogs have been published. For example, cryptophycins have been synthesized by a convergent method in which four components, Unit A, Unit B, Unit C, and Unit D (Golakati et al., 1995, J. Am. Chem. Soc., 117(49):12031), are coupled together to form the final product (see, for example, U.S. Pat. No. 6,013,626). In other methods, novel semi-synthetic compounds are generated, for example, by converting the epoxide of a natural cryptophycin to a carbon-carbon double bond (see, for example, U.S. Pat. Nos. 4,845,085 and 4,845,086). Stereo-selective addition of functional groups is often problematic during chemical synthesis of cryptophycins, however. Therefore, few of the methodologies for cryptophycin syntheses are considered viable or practical on a commercial scale.